Which ingredient is NOT typically part of traditional pesto?

Traditional pesto is a sauce originating from the Italian region of Liguria and is primarily made with basil, garlic, pine nuts, Parmesan cheese, and olive oil. Each of the other ingredients listed plays a significant role in authentic pesto. Garlic adds aromatic flavor, pine nuts contribute a creamy texture and rich taste, and cheese, typically Parmesan, provides the necessary depth and saltiness.

Butter is not a typical ingredient in traditional pesto recipes. While variations of pesto can include different nuts, herbs, or even other oils, butter is not a component of the classic formulation. This distinction highlights the essential qualities and characteristics of traditional pesto that set it apart from other sauces.